The present invention relates to a method for improving the melt viscosity of polyetherimides by incorporating long chain alkylamine chain-stoppers during the melt polymerization of aromatic bis(ether anhydride) and aromatic diamine used in the production of such polyetherimides, or during the formation of polyetherimide prepolymers.
Prior to the present invention, as shown by copending application Ser. No. 37,438, filed May 9, 1979 and assigned to the same assignee as the present invention, injection moldable polyetherimide oligomers were made by effection reaction between substantially equal molar amounts of organic dianhydride of the formula, ##STR1## and organic diamine of the formula, EQU H.sub.2 N--R--NH.sub.2, (2)
under interfacial polymerization conditions, where Z is a member selected from ##STR2## and divalent organic radicals of the general formula, ##STR3## where X is a member selected from the class consisting of divalent radicals of the formulas, ##STR4## where y is an integer from 1 to 5, and R is a divalent organic radical selected from the class consisting of aromatic hydrocarbon radicals having from 6 to about 20 carbon atoms and halogenated derivatives thereof, alkylene radicals having from 2 to about 20 carbon atoms, cycloalkylene radicals having from 3 to about 20 carbon atoms, from C.sub.2 to about C.sub.8 alkylene terminated polydiorganosiloxane and divalent radicals of the formula, ##STR5## where Q is a member selected from --O--, --S--, --SO.sub.2 --, --CO--, and --C.sub.x H.sub.2x --, x is an integer from 1 to 5 and a is 0 or 1.
Although the above described polyetherimides consisting essentially of chemically combined units of the formula, ##STR6## where R and Z are as previously defined, can be used as high performance injection moldable thermoplastics, the zero shear viscosity of the resulting thermoplastic can be 15.8.times.10.sup.5 poise at 300.degree. C. Even though the aforementioned thermoplastic materials have valuable injection moldable characteristics, those skilled in the art know that the aforementioned zero shear viscosity is undesirably high for particular applications. In addition, the resulting molded parts are often found to adhere to the surfaces of the mold resulting in complications in fabrication. In addition, the surface characteristics of the polyetherimide often did not satisfy the requirements of the fabricator in instances where a glossy appearance was required. The present invention is based on the discovery that polyetherimides, consisting essentially of units of formula 3 having a significant reduction in melt viscosity during melt polymerization and improved mold release and surface characteristics can be made by utilizing an effective amount of a long chain aliphatic hydrocarbon alkyl amine of the formula, EQU R.sup.1 --NH.sub.2, (4)
where R.sup.1 is a aliphatic radical having from 12-20 carbon atoms, during the melt polymerization of substantially equal molar amounts of the organic dianhydride of formula (1) and organic diamine of formula (2).